Although it can be applied to any desired large-area fibre-composite structural components, the present invention and the problem on which it is based are explained in more detail with reference to the rear pressure dome, i.e. the dome of the rear pressure bulkhead, of an aircraft.
In the production of structural components in the aircraft sector, on the one hand certain weight specifications have to be observed, but on the other hand the production of such structural components must also be economical. In the aerospace industry, composite materials are increasingly replacing metal materials, since they are much lighter than metal materials. Every kilogram of weight that is saved advantageously reduces fuel costs or increases the payload.
For example, lightweight carbon-fibre reinforced plastics (CRP) are used for the production of wing trusses, landing flaps, rear fuselage sections with horizontal and vertical tail empennages and the aforementioned pressure dome. For economic reasons, airliners fly at altitudes of about 10 to 15 km. To be able to survive at these altitudes, a pressurized cabin is required. In this, a pressure that corresponds to a flying height of approximately 3 km is maintained. The pressure dome forms the rear end part for this pressurized cabin. During the flight, it bears the entire internal cabin pressure. Together with a ring of titanium, for example, and numerous angles for introducing force into the fuselage structure, the dome is mounted in a clamped manner on the assigned ring in front of the vertical empennage.
For components of a large area and little curvature, such as for example the empennage panels, at present resin-impregnated carbon fibre strips (known as prepregs) are used. These are laboriously brought into the later shape and cured by means of pressure and heat in what is known as an autoclave.
However, the methods so far known to the applicant for the manual laying of the prepreg strips are mainly suitable for geometries that are simple and have little curvature. In the case of more complex geometries to be laid, the laying rate is reduced to a value that is no longer economical. Furthermore, the pre-impregnated prepreg strips are relatively expensive and can only be stored under certain conditions.
For structures that have a greater curvature or are more complex, the applicant has developed a novel production concept, which is mentioned in the trade journal HIGH PERFORMANCE, Composites May 2003, page 45 et seq.; the trade journal Forum, July 2004, page 8 et seq. and in the trade journal Innovate!, “Flugzeugbau mit Nadel und Faden und neuen Werkstoffen” [aircraft construction with needle and thread and new materials), page 24 et seq. Resin-free carbon fibre fabrics are accordingly brought into the desired shape in the dry state, the resin only being subsequently worked into the fabric. Resin-free carbon fibre fabrics can be handled much more easily than sticky prepreg strips. Individual, multi-axial carbon-fibre nonwoven fabrics are sewn together by means of an automated sewing method to form a so-called nonwoven carpet. In this nonwoven carpet, the carbon fibres are arranged in the longitudinal and transverse directions. The individual multi-axial carbon-fibre nonwoven fabrics or semifinished fibrous sheets are therefore joined together, for example by sewing, to form large-area, planar nonwoven carpets, rolled up on rolls and unrolled over a shaping element.
When using previous laying techniques and installations for laying the sewn carpets made up of individual multi-axial nonwoven sheets, one problem would be that undesired folds or waves would form, in particular in the edge regions, when the nonwoven carpets are laid on highly curved shaping elements. The formation of such folds makes it considerably more difficult to place the finished structural components against assigned mounting parts during final assembly.